With increasing a population of aged generation, dementia is occupying large weight in care of the aged. Although many medicines have been developed in order to improve various types of dementia such as dysmnesia, they are not fully enough in the points of efficacy, persistence and side effect.
For example, the function of cholinergic nervous system in hippocampus, amygdala and cerebral cortex is depressed in brains of patients of Alzheimer's disease (Pope et al., Trans. Am. Neurol. Assoc., 89, 15 (1964), Bowen et al., Brain, 266, 558 (1976) and Davies et al., Lancet, ii, 1043 (1976)). The above-mentioned is considered to be firmly concerned with nosogenesis of the impairment of memorization or memory which is main symptom of Alzheimer's disease (Whitehouse et al., Science, 215, 1237 (1982)). Therefore, there a possibility that these disturbances are improved by potentiating cholinergic nervous system. However, agonists of muscarinic cholinergic receptor which have been used up to date have high toxicity in spite of showing efficacy and therefore have not been practically used (Wettsein et al., Psychopharmacology, 84, 572 (1984) and Hollander et al., Biol. Psychiatry, 22, 1067 (1987)).
So, more effective and safe medicaments are required for the above-mentioned diseases.
As a result of continuous effort and detailed investigation of the present inventors in view of the above-mentioned actual circumstances, it has now been found that a novel bicyclic compound containing nitrogen atom and a salt thereof show anti-amnesic activity by oral administration in animal experiments such as experimental amnesic mice, that the above-mentioned compounds potentiate central cholinergic neural function as a characteristic of anti-amnesic activity by acting on muscarinic cholinergic receptors and that toxicity of the above-mentioned compounds is low. Therefore the above-mentioned compounds have been found to be useful as a cognition enhancer, and thus the present invention has been accomplished.